Phil, We’ve never used our shower either but water does sometime make it into the shower/head sump. We have a pump that draIns those sumps that empties into the sink in the head. Is it possible the connections under the sink for the cold fresh water and the sump drain connection got swapped? Seems unlikely but … Hope you’re having a good season. Dave
David Young
Bay Cat, 30U #402
Suttons Bay, MI
USA
Assuming the water passed through a faucet or shower head I’d target the fresh water source. I had a similar problem decades ago and quickly realized we had not shocked the fresh water system with bleach that year nor added a splash to the fresh water tanks when filling them. We don’t drink the water in the fresh water tanks nor do we add too much bleach , but just enough to offset the Ph level to prevent algae from forming.
You may be fortunate that you’re at the tipping level of a full bloom vs light case of algae. Drain all tanks, and look up ‘shocking your water system’ to get the correct ratio of bleach to water. There are other methods as well if you don’t care to use bleach. Regards, Gary/Aloki
Practical Sailor has a good article on treatment. Gallons X .13 = oz of bleach (1/8 cup of bleach for 10 gallons) and let it sit for four hours.
https://www.practical-sailor.com/systems-propulsion/preventing-and-treating-the-tainted-tank